Method for making gravel filters in oil wells

ABSTRACT

A method for making gravel filters in oil well bores by ascertaining the location of a producing formation adjacent to a cemented casing in a well bore. Water formation may exist between oil formations. The next step involves cutting a portion of the casing adjacent to the producing formation. A section mill equipment is used to cut, continuously, the cemented casing. The bore adjacent to the producing formation is enlarged. An underreamer is utilized to remove the surrounding cemented space and enlarge the oil well diameter. Then a sufficient amount of gravel is deposited in the enlarged portion of the bore to create an effective filter for a producing tube with a screen at its distal end positioned adjacent to the cemented bottom of the well bore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for making gravel filters in oil well bores, particularly in those oil well bores where there are water veins near oil producing formations.

2. Description of the Related Art

Some producing formations tapped by oil well installations have sandy characteristics that require the creation of gravel filters adjacent to the producing formation. The present methods typically gun the casing to make holes that connect the producing tube with a gravel filter that is defined by the inner surface of the well bore and the outer surface of the casing. This results in a very limited and thin gravel filter that is susceptible to getting clogged thereby frequently interrupting the operation of the well. The method is also not very precise.

Several methods for making gravel filters in oil well bores have been used in the past. None of them, however, have the flexibility and precision, nor the effectiveness (from its larger size), of the present method. Additionally, this method can be used in new and old oil wells, including those where the gun method was used. The precision characteristics of the present method are quite desirable in oil wells with water veins in relative proximity to the oil producing formation.

Applicants believe that one of the related references corresponds to U.S. Pat. No. 2,371,385 issued to Eckel in 1942 for a gravel packed liner and perforation assembly. Eckel's patent discloses the use of a gun perforator 21 that is suspended by a cable 24 within a liner or casing 11. The latter includes an envelope carrying the granular material or gravel 17. The difficulties with the uncertain path of the bullets passing through granular material 17 are documented by the patentee. Page 2, Col. 3, lines 25-32. Another problem with present gunned oil well casings is that the gravel material needs to be selected so that it is smaller than the unpredictable perforations. In sum, there is little control or precision to anticipate the resulting openings with gun operated procedures.

Other patents describing the closest subject matter provide for a number of more or less complicated features that fail to solve the problem in an efficient and economical way. None of these patents suggest the novel features of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

With the above and other related objects in view, the invention consists in the details of construction and combination of parts as will be more fully understood from the following description, when read in conjunction with the accompanying drawings in which:

FIG. 1 represents an elevational cross-sectional view of an oil well bore B with a new (unused) casing 20 and a cemented bottom. A producing formation and a water vein above it are also represented to show typical characteristics in an oil well.

FIG. 2 shows an elevational representation similar to the one shown in the previous figure with a section mill tool positioned to start cutting through the casing.

FIG. 3 illustrates another elevational view similar to the previous figures with the blades cutting through the casing.

FIG. 4 is a representation of an elevational view of the well's bore with the tool section milling the casing.

FIG. 5 shows a cross-sectional view of the well's bore except for the underreamer tool for which the cross-section is not shown. The underreamer is shown enlarging the bore in a predetermined location.

FIG. 6 shows an elevational view of the well's bore with a tool forming a gravel-packed filter between the enlarged portion of the bore and the casing.

FIG. 7 represents another elevational view of the well's bore shown in the previous figures with a producing tube in place that includes a screen through which the filtered sand with oil is passed.

FIG. 8 shows an elevational view of a conventional oil well as it exists in the prior art.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, where the relevant portion of an oil well installation is generally referred to with numeral 10, it can be observed that it basically includes casing 20 that extends coaxially inside bore B that includes a cemented bottom b, as it is typically found in new oil well installations. Bore B typically passes through water formations W and oil producing formations O. The space S between casing 20 and bore B is typically cemented to keep casing 20 in place. The lowermost end 22 of casing 20 is typically brought against bottom b. Several tools are then inserted in casing 20 and lowered to the required locations and finally the producing casing is installed.

In old oil well installations, a filter has been previously made with a gun perforator that caused holes 23 to be made through casing 20 at predetermined locations, as shown in FIG. 8. The explosives used penetrate through cemented space S. The present invention can also be used to repair these conventional operating oil well installations.

The first step in the present method is to ascertain the location where the window for the filter is to be made or where the repair is to take place. Once this is determined, a section milling tool is lowered to that location and casing 20 is cut, creating an interruption. The cutting takes place with precision that is not possible with the gunning method. In this manner, a user can avoid water formations W. Casing 20 is kept in place since the annular space between casing 20 and the surface of bore B has been cemented, as it is conventionally done in the industry. A section milling tool, like the one described in U.S. Pat. No. 6,920,923, can be used to perform this function. A section milling tool is used to cut casing 20 and concentrates its blades' action on this operation.

The next step, after withdrawing the section milling tool 30, is the lowering of the underreamer 40 to the location where the window was formed. An underreamer, like the one described in Applicant's U.S. Pat. No. 5,896,940, can be used for this step. The underreamer enlarges the diameter of the bore at a location adjacent to where the window 25 was formed as it can be seen in FIG. 5.

After retrieving underreamer 40, a setting tool 50 is lowered and a mix of gravel and a fluid is pumped radially through window 25, as seen in FIG. 6. The fluid can be water or other suitable liquid conventionally used to carry granular material, such as gravel, in oil well installations. Once a sufficient amount of the gravel mix 70 is pumped in the enlarged portion of the well, setting tool 50 is retrieved and producing tube 60 is installed. The result is a considerably larger volume of gravel filter 80 with an extended life, as best seen in FIG. 7.

Producing tube 60 includes a screen 62 with through holes 64 cooperatively smaller than the diameter of the granular material constituting the annular filter to prevent this material from entering producing tube 60. Different types of producing tubes 60 are conventionally used.

One of the advantages of the present method for creating a gravel filter is its precision. A user can control the dimensions of the window or windows to be built in casing 20. The size of the gravel used can also be controlled thereby knowing what the characteristics of the filter will be. The present methods for building gravel filters at present involve gunning a portion of casing 20 with unpredictable locations and dimensions for the holes.

The foregoing description conveys the best understanding of the objectives and advantages of the present invention. Different embodiments may be made of the inventive concept of this invention. It is to be understood that all matter disclosed herein is to be interpreted merely as illustrative, and not in a limiting sense. 

1. A method for making gravel filters in oil wells having a casing coaxially mounted within a well bore and defining a space between said bore and said casing that is cemented to keep said casing in place, comprising the steps of: A) ascertaining the location, at the cemented casing in an oil well bore, adjacent to a producing formation where a gravel filter is to be built; B) cutting a continuous portion of said casing adjacent to said producing formation; C) enlarging said bore's diameter where said portion was cut to create an enlarged annular space by removing the cemented space adjacent to said portion and beyond the bore's initial diameter; D) lowering and installing a producing tube having a distal end with an intake screen and being coaxially disposed within said casing and positioning said intake screen substantially adjacent to said casing portion which was removed; E) depositing an effective amount of gravel in said enlarged annular space; and F) sealing said space between said bore and said casing at a predetermined distance above said portion.
 2. The method set forth in claim 1 wherein the steps of cutting said casing and enlarging said bore's diameter is performed with a section mill and an underreamer.
 3. The method set forth in claim 2 wherein the gravel is selected for predetermined diameters in accordance with the characteristics of said producing formation. 